G stands for the Gorgons

The Gorgons are three sisters, daughters of ancient gods, Phorkys and Keto. The sisters Sthenno and Euryale were immortal but the third, Medusa, was mortal. All three were so hideous, the shock of seeing them would turn anyone to stone. They were said to have snakes for hair. Medusa is called The Gorgon or sometimes just Gorgon.